Why: Keys must be added without writing masks back, and a turn needs copy, exclude, and regenerate without deleting history.
Evidence: npx tsc -b. Session notes and candidate switches call the new conversation and message routes.
Impact: Settings gains key, lore, and slash-template panels. Excluded messages stay visible and are dimmed.
Refs: docs/records/2026-10-04-sillytavern-review.md
